Aircraft fluid jet reaction engines

ABSTRACT

An aircraft fluid jet reaction engine having an exhaust nozzle which has means for supplying fuel to form a combustible mixture with the local atmosphere which is ignited by contact with the hot gas efflux from the exhaust nozzle and is burnt externally of said gas efflux. The burning mixture raises the static pressure at the region downstream and adjacent the exhaust nozzle thus reducing base drag and also acts to suppress noise from the gas efflux. Igniter means are provided for initiating and maintaining combustion. Fuel to form the combustible mixture is fed through fuel nozzles, in the engine structure at its downstream end, and upstream thereof both externally and internally of the exhaust nozzle.

- United States Patent [73] Assignee Minister of Technology in HerBritannic Majesty '5 Government of the United Kingdom of Great Britainand Northern Ireland London, England [32] Priority July 15, 1968 [33]Great Britain [31] 33,543/68 [54] AIRCRAFT FLUID JET REACTION ENGINES 8Claims, 1 Drawing Fig.

[51] Int. Cl F02k l/00, F02k 3/10 [50] Field of Search 60/231,

[56] References Cited UNITED STATES PATENTS 2,653,445 9/1953 Halford eta1 60/261 X 2,952,123 9/1960 Rich 60/231 3,010,280 11/1961 I-lausmann...60/271 X 3,034,294 5/1962 Brown 60/271 X 3,132,476 5/1964 Conrad.....60/231 X 3,363,421 1/1968 Ferri 60/270 X Primary Examiner-Al LawrenceSmith Attorney Stevens, Davis, Miller & Mosh e r ABSTRACT: An aircraftfluid jet reaction engine having an exhaust nozzle which has means forsupplying fuel to form a combustible mixture with the local atmospherewhich is ignited by contact with the hot gas efflux from the exhaustnozzle and is burnt externally of said gas efflux. The burning mixtureraises the static pressure at the region downstream and adjacent theexhaust nozzle thus reducing base drag and also acts to suppress noisefrom the gas efflux.

Igniter means are provided for initiating and maintaining combustion.

Fuel to form the combustible mixture is fed through fuel nozzles, in theengine structure at its downstream end, and upstream thereof bothexternally and internally of the exhaust nozzle.

AIRCRAFT FLUID JET REACTION ENGINES This invention relates to aircraftfluid jet reaction engines.

In one aspect the invention is concerned with aircraft having suchengines and which are required to fly within a speed range extendingfrom takeoff speed at least to transonic speeds and perhaps beyond tosupersonic speed.

For aircraft having air-breathing fluid jet reaction engines anddesigned for transonic or supersonicflight speeds, it is known that theexit area of the engine exhaust nozzle best suited to high flight speedsis too large at lower flight speeds and in consequence, incurs at suchlow speeds a base drag due to overexpansion of the exhaust jet and/orseparation of the flow from the inner surface of the exhaust nozzle.

Proposals have been made for providing a variable shape and exit areanozzle with a view to alleviating these difficulties, the configurationof the nozzle being changed for differing flight speeds so that the flowwithin it more nearly approaches an ideal. Such arrangements add weight,are complicated and therefore form a safety and economic liability.

Even if a variable exit area nozzle is used the datum outer baseperipheral area of the main structure at its downstream end will usuallyremain constant as the exit area of the nozzle is reduced and hencethere will be a corresponding increase in the base area between thenozzle and main structure which will have induced upon it low pressuresand consequent base drag. I

In the case where a fully variable exit area nozzle is not used there isa section of the inner wall of the nozzle, at its rearward end at least,at which overexpansion, and possibly separation, turbulence andrecirculation occur.

Thus, in the case of the fixed exhaust nozzle or a variable area exhaustnozzle a region of low pressure is created which causes suction or basedrag at the aft end of the enginenozzle.

With the advent of large high speed aircraft having large high poweredjet engines the problem of aircraft noise has become of increasingimportance to the extent that the frequency of aircraft takeoff andlanding movements at airfields in residential areas is in somecases-limited at least during the normal sleeping hours of say midnightuntil early morning.

It is known that a large proportion of aircraft noise results from theturbulent mixing of propulsive jets from engine exhaust nozzles with thelocal free-stream or low speed secondary airflows and it has previouslybeen proposed to use acoustic shrouds containing sound insulatingmaterial which act to muffle or reflect those parts of the noise fieldwhich would otherwise radiate towards populated areas. The use of suchshrouds is inhibited for practical reasons as they entail increasedcost, weight and drag.

It is an object of the present invention to provide means whereby thebase drag of an aircraft fluid jet reaction engine may be reduced to alower level than would otherwise exist and the noise radiated from theengine efflux is reduced.

An aircraft air-breathing fluid jet reaction engine having an engineexhaust nozzle according to the present invention has means forsupplying fuel to form a combustible mixture which is ignited and burntat least in the region to the rear of the engine exhaust nozzle at whicha low pressure and hence base drag would otherwise develop.

The fuel fed into said region and/or to the local atmosphere surroundingthe aft region of the nozzle mixes and forms a combustible mixture whichis ignited by the hot exhaust gases from the engine; the burning mixturehas the effect of raising the pressure in the region to the rear of theengine nozzle and local structure and between the exhaust flow and theinner wall of the nozzle, where low pressure and base drag wouldotherwise develop, such that there is a reduction in base drag which maybe such that an actual base thrust is obtained; the burning mixture alsoforms a layer of burning gases between the efflux from the jet engineand the local free-stream or secondary flow. This has the effect oflengthening the interface between the jet efilux and the localfree-stream or secondary flow. Two interfaces will in fact now bepresent, one between the jet efilux and the burning gas mixture and onebetween the latter and the local free stream or secondary flow. Theoverall effect is a reduction in turbulence intensity and hence areduction of noise output. Furthermore the layer of burning gases willitself act as a muffler which by producing multiple reflections'of soundfrom the jet efflux within the layer will reduce the noise to lower andless offensive frequencies or reflect it upwards.

Provision may be-made for initiating and/or sustaining ignition of thecombustible mixture in addition to the effect of the hot engine exhaustflow and may comprise igniter of glow plugs at the outer and/or aftsurface of the structure surrounding the engine, and/or within theengine exhaust nozzle.

The fuel fed into the local atmosphere may be the same as that suppliedto the propulsion engine or may have additives or be a different fuelsuch as low flash point gasoline which renders ignition more easilyobtainable, and/or burning more intense or more efficient.

To promote burning within said low pressure region and particularlywithin the engine exhaust nozzle itself, fuel may be fed directly intosaid region either alone or with air, in addition to that fuel suppliedupstream of said region.

The fuel fed into the local atmosphere surrounding the aft region of thenozzle may be injected into or through the boundary layer of thestructure surrounding the engine and may have provision for inducingmixing of the fuel with the air such as swirl nozzles.

Injection of the fuel will be far enough upstream of the base dragregion to give sufficient time for a correct fuel air mixture todevelop.

Thus, in the case of a front-fan jet engine installation, fuel injectionmay conveniently be from the struts supporting the fan cowl and'frompositions possibly outside the engine boundary layer.

In cases where the reduction of jet efflux generated noise is of primeimportance the fuel may be injected and burnt to form a layer of burninggases beneath the jet efflux whereby noise is prevented from beingradiated downwards.

An example of the invention is illustrated by the accompanyingdiagrammatic drawing which is a cross section side elevation of the rearsection of an aircraft air-breathing jet reaction engine axisymmetricexhaust nozzle.

The rear section of the engine exhaust nozzle is shown at l l and hasinner, outer and end walls 12, 13, and 14 respectively. Three annularseries of fuel injector nozzles 15, are provided in the inner wall 12,the outer wall 13 and the end wall 14. lgnitor plugs 16 are located atthe surface of the inner, outer and end walls 12, 13, 114. A fuel pump17 has fuel lines 18 leading to the fuel nozzles 15.

At flight speeds below the aircraft speed for which the duct isdesigned, e.g. at transonic and lower air speeds for a supersonicaircraft, the exhaust flow from the duct tends to break away from theinner wall 12 at A, A and then forms a gas stream having a boundary asshown by the dotted lines B. As a result there is a region of lowpressure recirculation, as shown by the arrows C between the inner wall12 and the exhaust jet which causes base drag. Even without thiscirculation, a low pressure will develop immediately downstream of theend wall 14, which will also cause base drag.

With the arrangement according to the invention fuel is supplied by thepump 17 through the fuel lines 18 and nozzles 15 and issues into andpossibly through the boundary layer at the duct outer wall 13 into thelocal atmosphere surrounding the aft region of the nozzle into theregion to the rear of the end wall 114 and into the region of lowpressure recirculation C where it forms a combustible mixture within theregion shown generally by chain dotted boundary lines B and D.

This mixture is ignited by contact with the hot exhaust gas stream Band/or by the action of the igniter plugs 16. The resulting pressurerise following ignition raises the pressure in the region of C, C anddownstream of the end wall 14, 14, with a consequent reduction in basedrag or even the provision of actual thrust.

To avoid shocks and/or separations due to fuel injection, the fuel maybe directed by nozzles such as 15 tangentially with or obliquely to thewalls 13 but in practice however, the production of shock compressionmay increase the efficiency of base burning and so be a desirablefeature in which case fuel injection will be normal to the flow asshown.

It may be that combustion will be desired over the outside surfaces 13,13 so that afterbody drag at this region is also overcome and basethrust increased.

Provision may be made for injecting air through nozzles similar to thefuel nozzles 15 to form a combustible mixture with the injected fuel andmay comprise an air pump 19, air line 20 and air directing nozzle 21.

I claim:

1. An aircraft fluid jet reaction engine comprising: an engine exhaustnozzle, at least one supply line for fuel, fuel directing meansterminating said fuel supply line at the outer wall surface of thedownstream end region of said exhaust nozzle, and means for supplyingfuel through said supply line and said fuel directing means into thelocal atmosphere externally of said exhaust nozzle to form a combustiblemixture which is ignited by contact with the hot gas efflux from theengine exhaust nozzle and burnt externally of said gas efilux.

2. An engine as claimed in claim 1 having a rear end wall structure atthe downstream end of said exhaust nozzle,

fuel-directing means supported in said structure for directing fuel tothe rear of said structure, fuel supply lines terminating at saidfuel-directing means, further structure forwards of said end wallstructure having further fuel-directing means for directing fuel intothe local atmosphere adjacent said further structure, and,

further fuel supply lines terminating at said further fueldirectingmeans.

4. An engine as claimed in claim. 1 having supply lines for air,

air-directing means terminating said air supply lines. in the region ofsaid fuel-directing means, and, means for supplying air through said airsupply lines and said air-directing means to mix with the fuel issuingfrom said fuel-directing means.

5. An engine as claimed in claim 1 and having igniter means supportedadjacent said fuel-directing means and operative to supplement theignition effect of the hot gas efflux from the engine exhaust nozzle toinitiate and maintain combustion of said combustible mixture.

6. An engine as claimed in claim 2 having exhaust noule fuel-directingmeans supported in said engine exhaust nozzle adjacent its downstreamend for directing fuel into the region bounded by said nozzle, and, fuelsupply lines terminating at said exhaust nozzle fuel-directing means.

7. An engine as claimed in claim 6 having supply lines for air,air-directing means terminating said air supply lines in the region ofsaid fuel-directing means, and, means for supplying air through said airsupply lines and said air-directing means to mix with the fuel issuingfrom said fuel-directing means.

8. An engine as claimed in claim 7 and having igniter means supportedadjacent said fuel-directing means and operative to supplement theignition effect of the hot gas efflux from the engine exhaust nozzle toinitiate and maintain combustion of said combustible mixture.

1. An aircraft fluid jet reaction engine comprising: an engine exhaustnozzle, at least one supply line for fuel, fuel directing meansterminating said fuel supply line at the outer wall surface of thedownstream end region of said exhaust nozzle, and means for supplyingfuel through said supply line and said fuel directing means into thelocal atmosphere externally of said exhaust nozzle to form a combustiblemixture which is ignited by contact with the hot gas efflux from theengine exhaust nozzle and burnt externally of said gas efflux.
 2. Anengine as claimed in claim 1 having a rear end wall structure at thedownstream end of said exhaust nozzle, fuel-directing means supported insaid structure for directing fuel to the rear of said structure, fuelsupply lines terminating at said fuel-directing means, further structureforwards of said end wall structure having further fuel-directing meansfor directing fuel into the local atmosphere adjacent said furtherstructure, and, further fuel supply lines terminating at said furtherfuel-directing means.
 3. An engine as claimed in claim 1 having exhaustnozzle fuel-directing means supported in said engine exhaust nozzleadjacent its downstream end for directing fuel into the region boundedby said nozzle, and, fuel supply lines terminating at said exhaustnozzle fuel-directing means.
 4. An engine as claimed in claim 1 havingsupply lines for air, aiR-directing means terminating said air supplylines in the region of said fuel-directing means, and, means forsupplying air through said air supply lines and said air-directing meansto mix with the fuel issuing from said fuel-directing means.
 5. Anengine as claimed in claim 1 and having igniter means supported adjacentsaid fuel-directing means and operative to supplement the ignitioneffect of the hot gas efflux from the engine exhaust nozzle to initiateand maintain combustion of said combustible mixture.
 6. An engine asclaimed in claim 2 having exhaust nozzle fuel-directing means supportedin said engine exhaust nozzle adjacent its downstream end for directingfuel into the region bounded by said nozzle, and, fuel supply linesterminating at said exhaust nozzle fuel-directing means.
 7. An engine asclaimed in claim 6 having supply lines for air, air-directing meansterminating said air supply lines in the region of said fuel-directingmeans, and, means for supplying air through said air supply lines andsaid air-directing means to mix with the fuel issuing from saidfuel-directing means.
 8. An engine as claimed in claim 7 and havingigniter means supported adjacent said fuel-directing means and operativeto supplement the ignition effect of the hot gas efflux from the engineexhaust nozzle to initiate and maintain combustion of said combustiblemixture.